Solid fuel burners using pulverized coal, are well known in the art, see for example U.S. Pat. Nos. 988,271, 1,086,714, and 1,647,675. The '714 patent describes a shaping of a burner in such manner that its throat permits a larger amount of secondary air above and below the flame region than to the sides so as to shape the flame into a flatter form.
U.S. Pat. No. 4,297,093 describes a NO.sub.x reduction burner with which a fuel lean zone surrounds an inner fuel rich zone. A staging of combustion air in a burner to reduce NO.sub.x is described in U.S. Pat. Nos. 4,381,718, 4,422,391, and 4,426,939. In U.S. Pat. No. 4,654,001, NO.sub.x reduction is claimed for a coal burner by generating an outer fuel rich stream which surrounds an inner fuel lean stream. Multiple staging in a burner is described in U.S. Pat. No. 4,790,743.